RNA interference (hereinafter, referred to as RNAi) is a phenomenon in which translation is transiently inhibited by cleaving mRNA in a sequence-specific manner. An approach called knockdown, which causes this RNAi by introducing an RNA duplex such as short hairpin RNA (hereinafter, referred to as shRNA), has been established in various organism species. RNAi has been diffused widely, including study on its application to medical treatment, in a period as short as 10 years from its discovery as the convenient and potent approach of transiently inhibiting gene expression. However, its mechanisms or introduction techniques still remain to be evolved. Moreover, at this time, the theme of RNAi centers on studies for making knockdown strongly effective or the development of delivery techniques for delivering RNA to a site of interest.
Chung et al. have prepared artificial RNA in which the binding site of theophylline known as a caffeine-like low-molecular-weight compound has been introduced in the loop portion of shRNA, and have revealed that RNAi is inhibited in a theophylline concentration-dependent manner (see Non-Patent Document 1).    Non-Patent Document 1: Chung-Il An, Vu B. Trinh, and Yohei Yokobayashi, RNA, May 2006; 12: 710-716